1. Field of the Invention
This invention relates to reed switches in general and in particular, to the structure of cooperating electrical contacts of a reed switch.
2. Description of the Prior Art
The use of palladium as a contact material is desirable since the costs of other platinum group metals such as rhodium are relatively expensive. However, one known problem which occurs when platinum group metals are employed as reed switch contacts is that of "frictional polymer" formation. Frictional polymers form on the surfaces of contacts formed from platinum group metals when the contact surfaces have been "activated" by exposure to organic vapors or liquids such that an organic film covers the contact surfaces and the activated surfaces are rubbed against each other. It is only with the greatest difficulty that an electrical contact may be fabricated from certain metals of the platinum metal group without the contact surface becoming activated because our atmosphere contains a multitude of organic vapors which instantaneously cover any object exposed to the atmosphere. Because of the magnetostrictive properties of switch reeds which support the contacts of a reed switch, the contact surfaces rub against each other whenever the switch is operated.
Previous solutions to eliminate the problem of polymer formation where platinum group metals such as palladium are employed, utilize a protective layer of gold over one of the contacts. Essentially this approach results in a dissimilar contact pair, i.e., a gold surface of one contact contacting a palladium surface of the other contact. Other dissimilar contact pairs are taught by U.S. Pat. No. 2,793,273 issued May 21, 1975, to K. C. Underwood et al; U.S. Pat. No. 2,379,641 issued July 3, 1945, to C. W. Keitel; and U.S. Pat. No. 2,300,286 issued Oct. 27, 1942, to C. B. Gwyn. Such dissimilar contact approaches require selective assembly techniques which are not compatible with established reed switch fabrication techniques.
Another approach employs a protective layer of gold over both of the contacts such as taught by U.S. Pat. No. 3,671,702 issued June 20, 1972, to E. S. Penczek. This approach is undesirable for reed switch applications since gold contact surfaces have a tendency to stick.